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MATERIAL HANDLING—TRANSPORTATION OF SOLIDS
91
TABLE 7.—ECONOMIC SPEEDS OF BELT CONVEYORS HANDLING VARIOUS MATERIALS
different direction. Despite these limitations, they lend themselves to quite a variety of arrangements (see Fig, 3). The path of conveyors over curved inclines should be a catenary, but is quite generally made a circular arc of about 250 ft. radius. Installations of movable trippers and the first fixed dump require that the tail pulley of the conveyor be sufficiently removed that when the discharging device is at the limit of its backward travel the conveyor belt will not lift from the troughing idlers in the vicinity of the tail pulley.
The inclination of the pulleys of the troughing idlers turning up the edges of the belt affect the capacity of the conveyor, but as the capacity is so increased the power requirements increase more rapidly and also the wear on the conveyor belt. For this reason the degree of troughing has become pretty well standardized at an economic point with the end troughing pulleys turning up the belt to from 20 to 25 deg. With the degree of troughing so established, the capacity of the conveyor is controlled by the weight of the material handled and the belt speed. Table 7 lists the economic speeds for certain classes of material customarily handled on belt conveyors and Table 8 gives the average capacity of standard sizes of conveyors when continuously and uniformly loaded with material weighing 100 Ib. per cubic foot, while Formula (7) gives the equation for calculating the capacity of troughed belt conveyors handling
	Average	
	weight	Belt
Material	pounds per	speed feet per
	cubic	minute
	foot	
Coke ................	33.5	250
Broken stone (coarse) . .	165.0	275
Lump coal            ....	55 0	275
Ashes . .    .   .      .....	45.0	300
Lime and cement ......	65.0	300
Ore (average)	125 0	350
Crushed stone	160 0	375
Sand and gravel .......	110.0	375
Fine coal              .     . .	50.0	400
		
material of known weight at any given speed.
W =
KvfiVw
100,000 W = Capacity in tons per hour.
Formula  (7)
TABLE 8.—CAPACITY OF BELT CONVEYORS AT 100 FT. PER MINUTE Material weighing 100 Ib. per cubic foot
Width of belt, inches	Tons per hour	Width of belt, inches	Tons per hour
12	20.0	26	96.0
14	27.0	28	108.6
16	35.7	30	126.8
18	45.0	32	143.5
20	55.6	34	160.0
22	67.7	36	183.0
24	80.0	42	265.0